This application is based on application No. 98-9632 filed in the Korea Industrial Property Office on Mar. 20, 1998.
(a) Field of the Invention
The present invention relates to a method of preparing rubber substrate, and more particularly, to a method of preparing rubber substrate being capable of manufacturing rubber latex having large size and narrow distribution of the rubber particle size.
(b) Description of the Related Art
Graft polymers such as ABS (acrylonitrile-butadiene-styrene) are well known in the polymer industry, as are methods for their preparation, and are advantageous for use in various applications. Generally, the ABS graft polymers (resin) contain rubber substrates or backbone portion formed of a conjugated diene such a butadiene, and a grafted portion.
The impact resistance of the ABS resin is affected by size and distribution of the rubber substrate particles. For increasing impact resistance of the ABS resin, particle size of the rubber substrate particle for preparing the ABS resin should further increased.
In order to increase size, the rubber substrate particles are contacted with acidic materials, such as acetic acid or phosphoric acid, lowering pH of the particles and coagulating the particles. As the particles are coagulated with each other, particle size increases. In the present application, rubber substrate means rubber latex having small particle size before coagulation and rubber latex means rubber latex having large particle size after coagulation. The above methods are disclosed in Japanese Patent laid-open Nos. Sho 63-132903, Sho 63-117005, Hei 7-157501, and Japanese Patent Nos. Hei 2-9601, Sho 55-19246 and Sho 42-3112.
The size and distribution of rubber latex particles obtained by the above method are affected by the acidic material content and the gel content of rubber substrate particles. If the gel content is higher, the unwanted coagulum in the rubber latex is reduced, but particle size is smaller and particle size distribution is wide, lowering the impact resistance of rubber latex. If the gel content is smaller, the rubber latex has large particle size and a narrow particle size distribution, but an excess of coagulum occurs.
Furthermore, the gel content significantly depends on the reaction rate. Therefore, as the reaction rate elevates, the gel content increases and latex particle to be reacted is abundant. Due to these reasons, it is impossible to enlarge particle size during coagulation with the addition of acidic materials and make narrow particle size distribution.
It is object of the present invention to provide a method of preparing rubber substrates including a core and an outer layer, gel content of which are different.
It is another object of the present invention to provide a method of preparing rubber substrate having a large particle size and a narrow particle size distribution.
To accomplish these and other objects, the method of preparing rubber substrate includes the step of first-polymerizing 50 to 95 parts by weight of aliphatic conjugated diene monomer based on 100 parts by weight of total monomer, until the first-polymerized product has a gel content 5 to 70%.
Furthermore, the method includes the step of second-polymerizing the first-polymerized product with 5 to 50 parts by weight of monomer based on 100 parts by weight of total monomer.
One aspect of the present invention is to provide a method of preparing a rubber substrate. The method comprises first-polymerizing 50 to 95 parts by weight of an aliphatic conjugated diene monomer or a mixture of an aliphatic conjugated diene monomer and a copolymerizable ethylenically unsaturated monomer, thereby forming a core having a gel content; and second-polymerizing the core with 5 to 50 parts by weight of one or more monomers comprising an aliphatic conjugated diene monomer to form an outer layer on the core, thereby forming a rubber substrate comprising the core and the outer layer, wherein the parts of the monomers in the first and second polymerizing are based on 100 parts by weight of total monomers used in both of the first and second polymerizations. In the method, the rubber substrate has an average particle size of 600 to 1500 xc3x85. The rubber substrate has gel content of 60-95 wt %. The aliphatic conjugated diene monomer is at least one monomer selected from the group consisting of 1,3-butadiene, isoprene, chloroprene and piperylene. The copolymerizable monomer is selected from the group consisting of aromatic vinyl compounds, acrylate esters, methacrylate esters and vinylcyan compounds. The rubber substrate has a swelling index of 12 to 40. The gel content of the core is higher than a gel content of the outer layer. The one or more monomers comprise a mixture of an aliphatic conjugated diene monomer and a copolymerizable ethylenically unsaturated monomer. The gel content of the core is from 5 to 70 wt. %. The copolymerizable monomer is in an amount less than 20 parts by weight.
Another aspect of the present invention is to provide a rubber substrate prepared by the above-discussed method.
Still another aspect of the present invention is to provide a method of producing a rubber latex. The method comprises: preparing a rubber substrate by the above-discussed rubber substrate preparing method, and contacting the rubber substrate with an acid. In this method, the acid comprises acetic acid.
Still another aspect of the present invention is to provide a method of producing an acrylonitrile-butadiene-styrene (ABS) resin. The method comprises preparing a rubber latex using the above-discussed rubber latex producing method; and grafting styrene and acrylonitrile on the rubber latex, thereby producing an ABS resin. In the method, the grafting comprises reacting the rubber latex with a mixture comprising styrene and acrylonitrile.
Still anther aspect of the present invention is to provide an acrylonitrile-butadiene-styrene (ABS) resin produced by the above-discussed method of producing an ABS resin.
A still further aspect of the present invention is to provide a rubber substrate for use in producing an acrylonitrile-butadiene-styrene (ABS) resin. The rubber substrate comprises a rubber core and a rubber outer layer, each of which has a gel content, wherein the rubber core and outer layer are polymers of one or more monomers comprising aliphatic conjugated diene monomer, and wherein the gel content of the core is higher than a gel content of the outer layer. In the rubber substrate, the aliphatic conjugated diene monomer is at least one monomer selected from the group consisting of 1,3-butadiene, isoprene, chloroprene and piperylene. The one or more monomers comprise a mixture of an aliphatic conjugated diene monomer and a copolymerizable ethylenically unsaturated monomer. The copolymerizable monomer is selected from the group consisting of aromatic vinyl compounds, acrylate esters, methacrylate esters and vinylcyan compounds. The rubber substrate has an average particle size of 600 to 1500 xc3x85. The rubber substrate has gel content of 60-95 wt %. The rubber substrate has a swelling index of 12 to 40. The gel content of the core is from 5 to 70 wt. %.
The rubber substrate obtained by the method of the present invention has a core and an outer layer formed on the core. The gel content of the core is higher than that of the outer layer. Using the rubber substrate, a large particle size and a narrow particle size distribution rubber latex may be obtained. Furthermore, when ABS resin is prepared by using the rubber latex obtained, ABS resin having excellent impact resistance can be obtained.
The rubber substrate preparation method will be now described in more details.
50 to 95 parts by weight of monomer based on 100 parts by weight of total monomer is first-emulsion polymerized. The emulsion polymerization methods are well known in the art and generally include a detergent (a surfactant), an initiator and a molecular weight regulating agent in the emulsion polymerization medium.
The monomer may be only aliphatic conjugated diene monomer or a mixture of conjugated diene monomer and copolymerizable ethylenically unsaturated monomer. The conjugated diene monomer may be 1,3-butadiene, isoprene, chloroprene, piperylene, and comonomer thereof. The copolymerizable monomer may be aliphatic vinyl compounds such as styrene, xcex1-methylstyrene and vinylcyan compound such acrylonitrile. The copolymerizable monomer in the mixture monomer is less than 20 parts by weight.
The detergent may be alkyl aryl sulfonate, alkali metal sulfate, sulfonated alkylester, fatty acid soap, alkali salt of rosin acid such as potassium rosinate, alkai salt of olenoic acid such as potassium oleate and a mixture thereof. The detergent may present in the amount of 1 to 4 parts by weight.
The initiator may be water-soluble persulfate or peroxy compounds and water-solube redox systems. The persulfate may be sodium and potassium persulfate. The oil-soluble initiator may be cumene hydroperoxide, diisopropyl benzene hydroperoxide, azobisisobutyronitrile, tertiary butyl hydroperoxide, paramethanehydroperoxide, benzoyl peroxide and a mixture thereof. Besides, a mixture of water-soluble and fat-soluble radical initiators may be used. The amount of initiator may be 0.1 to 0.6 parts by weight.
The emulsion polymerization medium may be KCl, NaCl, KHCO3, NaHCO3, K2CO3, Na2CO3, KHSO3, NaHSO3, K4P2O7, Na4P2O7, K3PO4, Na3PO4, K2HPO4, Na2HPO4 and a mixture thereof. The amount of medium may be 0.2 to 1.0 parts by weight.
The molecular weight regulating agent may be n-octyl mercaptan, cyclohexyl mercaptan, dipentene dimercaptan, n-butyl mercaptan, n-dodecyl mercaptan, tertiary dodecyl mercaptan. The molecular weight regulating agent may present in the amount of 0.1 to 0.5 parts by weight.
The first-emulsion polymerization is carried out for about 5 to 15 hours at 50 to 70xc2x0 C. After the first-emulsion polymerization, the core of rubber substrate has a gel content of 5 to 70 wt %.
Thereafter, the core of the rubber substrate reacts with 5 to 40 parts by weight of monomer and 0.05 to 1.2 parts by weight of a molecular weight regulating agent to produce an outer layer on the core of the rubber substrate.
The gel content of the core is higher than that of the outer layer. The average particle size of the rubber substrate is 700 to 1500 xc3x85 and a distribution of particle size is less than 25%. Furthermore, the gel content of the rubber substrate is 70 to 99% and the swelling index of the gel is 16 to 40.
When such rubber substrate is used for preparing rubber latex, a rubber latex having a large particle size and a narrow particle size distribution can be prepared. As the rubber latex preparation method, the conventional method including the step of contacting the rubber substrate with acidic materials such as acetic acid may be used. As the rubber latex has a large particle size and a narrow particle distribution, ABS resin having excellent impact resistance can be prepared by using the rubber latex.